Clean up various use of escape/unescape functions for URL generation (#6334)

* Use PathUnescape instead of QueryUnescape when working with branch names

Currently branch names with a '+' fail in certain situations because
QueryUnescape replaces the + character with a blank space.

Using PathUnescape should be better since it is defined as:

// PathUnescape is identical to QueryUnescape except that it does not
// unescape '+' to ' ' (space).

Fixes #6333

* Change error to match new function name

* Add new util function PathEscapeSegments

This function simply runs PathEscape on each segment of a path without
touching the forward slash itself. We want to use this instead of
PathEscape/QueryEscape in most cases because a forward slash is a valid name for a
branch etc... and we don't want that escaped in a URL.

Putting this in new file url.go and also moving a couple similar
functions into that file as well.

* Use EscapePathSegments where appropriate

Replace various uses of EscapePath/EscapeQuery with new
EscapePathSegments. Also remove uncessary uses of various
escape/unescape functions when the text had already been escaped or was
not escaped.

* Reformat comment to make drone build happy

* Remove no longer used url library

* Requested code changes

routers/repo/pull.go

@@ -10,7 +10,6 @@ import (
 	"container/list"
 	"fmt"
 	"io"
-	"net/url"
 	"path"
 	"strings"
 
@@ -633,10 +632,7 @@ func ParseCompareInfo(ctx *context.Context) (*models.User, *models.Repository, *
 		infoPath   string
 		err        error
 	)
-	infoPath, err = url.QueryUnescape(ctx.Params("*"))
-	if err != nil {
-		ctx.NotFound("QueryUnescape", err)
-	}
+	infoPath = ctx.Params("*")
 	infos := strings.Split(infoPath, "...")
 	if len(infos) != 2 {
 		log.Trace("ParseCompareInfo[%d]: not enough compared branches information %s", baseRepo.ID, infos)